In the production of tert-amylphenols, o-tertamylphenol is by-produced. Although this o-tert-amylphenol can be used as a starting material for the production of 2,4-di-tert-amylphenol, it is difficult to separate it from p-tert-amylphenol. It is therefore preferred that byproduction of o-tert-amylphenol be reduced. 2,4,6-Tri-tertamylphenol has no value as a product and, therefore, it is desirable that the amount of 2,4,6-tri-tert-amylphenol formed be minimized as less as possible.
In recent years, 2,4-di-tert-amylphenol has been used, for example, as a starting material for the production of color formers for color photography and also additives for resins, and p-tert-amylphenols has been used, for example, as a starting material for oil-soluble dye intermediates and additives for lubricating oils.
High purity 2,4-di-tert-amylphenol or p-tertamylphenol is required in the above-described uses. In conventional methods, therefore, high purity isoamylene or tert-amyl alcohol is reacted with phenol to prepare the desired products. However, isoamylene and tert-amyl alcohol are expensive and are not readily available.
In order to overcome the above problem, a method has been proposed in which tert-amylphenols are produced from isoamylene contained in a C.sub.5 fraction from which isoprene had been extracted (see Japanese Patent Application (OPI) No. 35122/75 (the term "OPI" as used herein means a "published unexamined Japanese patent application")). In accordance with this method, after removal of isoprene and cyclopentadiene from the C.sub.5 fraction with maleic anhydride, the resulting C.sub.5 fraction is reacted with phenols in the presence of, for example, organic carboxylic anhydrides using sulfuric acid as a catalyst to produce tert-amylphenols.
This method, however, has several disadvantages. One of the disadvantages is that the yield of 2,4-di-tertamylphenol is low and the amount of o-tert-amylphenol by-produced which has no value reaches about 20%. Another disadvantage is that a neutralization/separation process is required due to the use of sulfuric acid as a catalyst. Moreover, in this method, the dienes contained in the C.sub.5 fraction are removed using maleic anhydride. This method takes a time as long as 16 hours until the reaction is completed.